Method of making compound gear



Aug. 13, 1963 L. c. FRIEND METHOD OF MAKING COMPOUND GEAR Filed April22, 1959 FICLL. FIG.2.

FIG. 6. 12 15 15 mwm FIG. 5

Ill

INVENTOR LINDSAY C. FRIEND ATTORNEY ted States Compound gears such asthose shown in FIGS. 1 and 2 of the drawing are usually made byinitially casting or forging a single solid body, then machining to therequired size, and cutting or hobbing in the teeth; or by initiallyforming (as by forging or casting or by cutting from rod stock), therespective gear bodies in separate parts, machining to size, and thenjoining one gear body to the other by 'splining, as by forcing a toothedend portion of the small pinion gear body into and through an undersizedcenter hole formed in the other gear body (which may be considered as aspur gear). To ensure against axial displacement, the projecting end ofthe pinion gear may be upset around the axis of the spur gear. Aconcentric arrangement is facilitated by hobbing the teeth of the piniongear before assembly and those of the spur gear after assembly, but thisis a matter of choice. If a compound gear made up of a single solid bodyis to be used in high-precision installations requiring cut teeth, itinvolves an expensive machining operation, which becomes more difiicultwhen the resulting gear is small or of the miniature type and requiresteeth for substantially the full length of the pinion gear; and it maybe necessary to machine away expensive metal. On the other hand, if thecompound gear is made by joim'ng two separately formed gears, one to theother, machining and scrap costs are reduced but a problem presentsitself in joining the gears in a manner such as to withstand torque andaxial loading at the point of jointure. Also, if the gears are joined bya tooth-splining operation under relatively great pressure, special jigsor tools may be required to hold the parts in concentric relation.

The primary object of the present invention, therefore, is to provide asimple method of fabricating compound gears which not only reduces thecost of fabrication but also insures a tight and lasting fit at thepoint of jointure. More specifically, the invention contemplates amethod of making compound gears by first fabricating the respective gearbodies or blanks separately and then joining them in a manner such asto, in effect, forge the gear bodies into an integral unit at the pointof jointure.

The method will be readily understood in view of the followingdescription taken in conjunction with the drawing, wherein:

FIGS. 1 and 2 are side and end elevations, respectively, of a compoundgear fabricated in accordance with the present method; it consists of apinion gear joined to a spur gear;

FIG. 3 is a view in perspective of the pinion gear body or blank readyfor the tooth-bobbing operation;

FIG. 4 is a disassembled view of both gear bodies ready for joining;

FIG. 5 is a central cross-section of the two gears at the start of thejoining operation; and

FIG. 6 is a similar view at the completion of the joining operation.

Referring to the drawing in detail, the pinion gear is indicated at 10and the spur gear at 11. The blanks for these may be made of anysuitable metal or material having the required deformationcharacteristics. Bronze or steel are commonly used. The operation startswith the making of a body or blank for each gear, which may be done byforging, casting, or cutting from rod stock. The blanks or bodies priorto joining are designated 10' and "atent 11. FIG. 3 shows the piniongear body ready for the tooth-hobbing operation; also compare with FIG.4 which shows the toothed pinion gear ready to be assembled to the spurgear body. Preferably, but not necessarily, the spur gear is not tootheduntil after the joining operation, since this method facilitates aconcentric unit. Note that the one end of the pinion gear body isprovided with a diametricallyred-ueed stepped projection consisting ofan undercut annular locking recess i=2 and an end guide shoulder orcollar 13. The shoulder or collar 13 functions as a guide and centeringmember when the pinion gear body or blankis positioned in the centerhole of the spur gear in preparation for the joining operation. This endpro-jectionmay be formed in any suitable manner, depending upon whetherthe blank is cast, forged or cut from rod stock. If cut from rod stock,the reduced end portion 13 and annular groove 12 may be formed by asimple machining operation, otherwise it may be initially cast orforged. The length of the projection, including the collar or shoulder13 and annular recess 12, is preferably substantially half the thicknessof the spur gear 11. However, the diameter and thickness of the collarand/or groove need not be highly precise; the dimensions of the collarmay be such as to permit it to move under a reasonable application offorce into the hole 1 4- with sufiicient snugness to ensure against playand the depth of the recess need only be sufiioient to receive excessmetal when the gears are joined as hereinafter explained. During thetooth-hobbing operation, a series of indentations or shallow teeth 13may also be formed in the periphery of the collar 13. While these arenot essential, they do assist in establishing a tight bond at the lineof jointure around the center hole of the spur gear.

FIG. 5 shows the pinion gear assembled to the spur gear ready for thejoining operation. Note that the shoulder or collar 13 centers thepinion gear with respect to the spur gear. The parts may then be putinto an arbor press and axial pressure applied until the end of thecollar is moved into a plane substantially flush with the outer surfaceof the spur gear. During this operation, metal is displaced from theadjacent or surrounding axial portion of the spur gear by the advancingflat end surfaces of the pinion teeth and this displaced metal in partenters the undercut or annular recess 12 and in part flows between and,in effect, merges with the teeth 13' of the pinion gear, note FIG. 6.The dimensions of the parts are preferably chosen such that the pinionteeth do not simply cut a splineway but also displace a certain amountof metal as above indicated, causing the metal at the joining area to beforged into the recess and the teeth to become embedded in the metal,positively locking the gears against both endwise and angulardisplacement, without any possibility of the slightest clearance or playat the point of jointure. It will also be observed that the outer endsurface of the spur gear comes flush with the end of the collar 13,requiring no machining to attain this result.

Actual experience with compound gears fabricated in this manner hasconclusively demonstrated that they possess considerable strength andresistance to relative torsional and axial displacement, and are capableof withstanding loads substantially equivalent to those of a compoundgear made from a single solid piece of metal or like material.

What is claimed is:

The method of fabricating a compound gear assembly which consists inperforming the following operations:

forming a first gear body with substantially axial teeth and an axialdiametrically reduced projection at one end thereof; forming a secondgear body with a smooth axial bore,

diameter of said projection and the axial dimension of which issubstantially greater than the axial dimension of saidprojection;forming an annular recessat the base of said projection where the teethof said "first gear terminate, leaving an annular guide portion at the,outer end of said a projection; J

and joining said gear bodies one to the other by insert-' ing the axialprojection of said first gear into the bore of the second gear andapplying suflicient axiallydirected pressure to cause the teeth of saidfirst gear to cut a splineway in the metal surrounding the bore of saidsecond gear and at the same time displace metal which in part passesinto the said recess and .in part substantially merges with the teethwhich have been driven into the second gear, said pressure beingmaintained until the outer end surface of said projection moves intosubstantially flush relation to the outersurface of said spur gear.

References Cited in the'file of this patent UNITED STATES PATENTS HartMar. 30, 1886 Hart Mar. 30, 1886 Coleman Sept. 8, 1914 Templeton June15, 1915 Bennett Oct. 26, 1915 Quegel et a1. May 9, 1922 Fulper Oct. 13,1925 Cullman July 29, 1930 Tarhox et a1. Sept. 2, 1930 Ronk Sept. 9,1930 Peterson Dec. 1, 1936 Sekella Feb. 22, 1938 Dingwerth Aug. 23, 1938'Neracher Mar..21, 1939 Madden Dec. 6, 1949 Klancnik July 17, 1956 Bantaet' a1 Sept. 23, 1958

